​​​​​​​Bovine H5N1 influenza from infected worker transmissible and lethal in animal models

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Monday, October 28, 2024

Bovine H5N1 influenza from infected worker transmissible and lethal in animal models

Some antiviral drugs highly effective against bovine H5N1

Colorized transmission electron micrograph of avian influenza A H5N1 virus particles (blue), grown in Madin-Darby Canine Kidney (MDCK) epithelial cells. Microscopy by CDC; repositioned and recolored by NIAID. Credit: CDC and NIAID

What

A highly pathogenic avian influenza (HPAI) H5N1 virus, isolated from the eye of a farm worker who became infected through contact with dairy cows, was lethal in mice and ferrets infected in a high-containment laboratory environment, according to a new study in Nature. The study investigators also found that the virus isolated from the worker, who experienced mild inflammation of the cornea (conjunctivitis), could be transmitted through the air between separated ferrets and might be capable of binding to and replicating in human respiratory tract cells.

The virus isolated from the worker is called huTX37-H5N1 and has a mutation (PB2-E627K) frequently seen in avian influenza viruses that replicate in mammals, typically making virus replication more efficient. These mutations underscore the need for continued monitoring and evaluation of viruses from the current H5N1 outbreak.

The study also showed that a bovine H5N1 virus is susceptible to the antiviral drugs favipiravir and baloxavir marboxil (brand name Xofluza) of the polymerase inhibitor class, as well as the neuraminidase inhibitor zanamivir. The virus is less sensitive to oseltamivir (Tamiflu), another neuraminidase inhibitor.

In laboratory experiments, huTX37-H5N1 replicated in human cornea and lung cells. The scientists determined the lethal dose of huTX37-H5N1 as less than 1 plaque-forming unit (PFU) in mice, compared to 31.6 PFU as the lethal dose of a bovine H5N1 virus isolated from the milk of a lactating cow. The huTX37-H5N1 virus also infected each of 15 different mouse tissues tested, with the highest virus levels found in respiratory tissues.

Researchers also infected ferrets with a high dose of huTX37-H5N1. Flu infections in ferrets more closely resemble human flu infections than those in mice. All infected ferrets died within 5 days and scientists found huTX37-H5N1 virus in all the tissues sampled, with high levels in the respiratory system. In a prior study, the researchers had infected ferrets with a bovine H5N1 virus and, although it caused severe disease, lethality was limited.

To evaluate respiratory transmission, the scientists placed healthy ferrets in cages about 5 centimeters away from ferrets infected one day earlier with one of four decreasing doses of huTX37-H5N1. All directly infected ferrets died within 6 days and, depending on the exposure dose, between 17% and 33% of the nearby animals became infected via respiratory droplet transmission. These results indicate that a bovine HPAI H5 virus isolated from an infected person can transmit among mammals via respiratory droplets, though with limited efficiency.

The authors note that the person infected with the huTX37-H5N1 virus did not develop severe illness. In fact, human cases reported from the current outbreak have mostly experienced conjunctivitis and/or mild respiratory symptoms. The researchers speculate that eye infection with a low dose of bovine H5N1 virus might result in localized conjunctivitis without severe disease in humans. Multiple exposures to seasonal human influenza viruses, they say, might provide people with low levels of protection against currently circulating HPAI H5N1 viruses—though additional study is needed.

In summary, this study characterizes the huTX37-H5N1 isolate, finding that it may be capable of replicating in cells of the respiratory tract in humans, that it is pathogenic in mice and ferrets, and that it is capable of being transmitted by the respiratory route in ferrets. The authors note that “based in these observations, every effort should be made to contain HPAI H5N1 outbreaks in dairy cattle to limit the possibility of further human infections.”

Scientists from the University of Wisconsin at Madison led the research with collaborators from Shizuoka and Tokyo Universities and the Research Center for Global Viral Diseases in Japan. The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, funded much of the work through its Centers of Excellence for Influenza Research and Response program. Articles


C Gu et al. A human isolate of bovine H5N1 is transmissible and lethal in animal models. Nature DOI: 10.1038/s41586-024-08254-7 (2024).

A Eisfeld et al. Pathogenicity and transmissibility of bovine H5N1 influenza virus in mice and ferrets. Nature DOI: 10.1038/s41586-024-07766-6 (2024).

...

https://www.nih.gov/news-events/new...ted-worker-transmissible-lethal-animal-models
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[Pathfinder]

H5N1 virus isolated from infected dairy worker is 100% lethal in ferrets, but does not appear to be circulating in nature anymore

October 28, 2024 By Will Cushman For news media

A dairy worker in Texas became infected with H5N1 avian influenza likely during the course of milking cows. A sample of the virus taken from the worker was 100% lethal in ferrets, though it spread inefficiently and does not appear to be continuing to spread. Photo: Althea Dotzour

A strain of H5N1 avian influenza virus found in a Texas dairy worker who was infected this spring was able to spread among ferrets through the air, although inefficiently, and killed 100% of infected animals in studies University of Wisconsin–Madison researchers performed with the strain earlier this year.

The good news: the dairy worker experienced mild symptoms and fully recovered, and the H5N1 strain that infected the worker does not appear to have continued spreading in the wild.

Still, the findings highlight the risks posed by a virus that continues to spread among dairy cattle and occasionally to farm workers, and the study’s lead scientist says he was surprised by the ease with which this particular strain was able to kill ferrets.

“This is one of the most pathogenic viruses I’ve ever seen in ferrets,” says Yoshihiro Kawaoka, a UW–Madison professor of pathobiological sciences who spearheaded the work, described Oct. 28, 2024, in the journal Nature.

Ferrets are a common model for studying how influenza viruses that primarily affect birds are able to adapt to mammals, a topic that Kawaoka and his colleagues at UW–Madison’s Influenza Research Institute investigate since such a jump could trigger an influenza pandemic.

Like other influenza viruses, H5N1 viruses mutate at a relatively rapid clip as they infect new hosts. Sometimes these mutations allow the viruses to more easily infect and spread among new species. That’s how the current viruses, which have been infecting birds around the world in recent years, began to spread among mammals, most notably North American dairy cattle in 2024.

Kawaoka and his collaborators found that the H5N1 virus that infected the Texas dairy worker included a mutation that the team first identified in 2001 as important for causing severe disease. Luckily, Kawaoka says, the strain with that mutation seems to have died out.

“This isolate is unique among the H5N1 viruses circulating in cows,” he says.

Kawaoka hypothesizes that H5N1 viruses took two paths when they made the jump from birds to cows, both facilitated by mutations that made the virus better adapted to mammals.

Kawaoka and his colleagues suggest that one path resulted in the more concerning mutation found in the Texas dairy worker, while the other led to a less dangerous mutation in the same protein.

“Both mutations give the virus the ability to adapt to mammals, but the good thing is the one containing this more pathogenic mutation has not been detected again,” Kawaoka says. “So there are no extremely pathogenic H5N1 viruses currently circulating in cows. However, if a currently circulating cow H5N1 virus acquires that mutation, then that would be an issue.”

Whether a virus with such a mutation would be dangerous for humans remains to be seen.

“The puzzling thing is why the human who got this virus did not have a severe infection,” says Kawaoka, noting a few possibilities.

Perhaps exposure to seasonal influenza viruses provides some level of protection via antibodies, or maybe the route of infection is important; the Texas dairy worker’s main symptom was conjunctivitis, suggesting the virus entered through the eye rather than the more typical respiratory route.

Alternatively, more robust surveillance of influenza cases among American dairy workers since the virus began spreading on farms might mean more cases — including mild ones — are being identified. Another possibility is this particular strain might simply be less severe in humans than mammals like ferrets.

“Those are all possibilities, but we don’t know,” says Kawaoka. “So, we’re now trying to understand why this virus is so pathogenic in ferrets and what that could mean for human infections.”
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https://news.wisc.edu/h5n1-virus-is...t-appear-to-be-circulating-in-nature-anymore/

 

[Michael Coston]

Nature: A Human Isolate of Bovine H5N1 is Transmissible and Lethal in Animal Models

Nature: A Human Isolate of Bovine H5N1 is Transmissible and Lethal in Animal Models

#18,369



Today the journal Nature has published a study which looked at the characteristics of the first H5N1 virus isolated in Texas from a dairy worker (huTX37-H5N1) which carried a worrisome mutation(PB2-E627K), but produced only mild symptoms in the index case.

In contrast to its mild presentation in the human, it proved lethal in both ferrets and mice, and it transmitted - with limited efficiency - via respiratory droplets to nearby ferrets.​

The study, which is behind a subscription paywall, can be accessed at the following link. Luckily, however, we have an excellent overview published today from the NIH.

Article Published: 28 October 2024​

A human isolate of bovine H5N1 is transmissible and lethal in animal models

• Chunyang Gu, Tadashi Maemura, Lizheng Guan, Amie J. Eisfeld, Asim Biswas, Maki Kiso, Ryuta Uraki, Mutsumi Ito, Sanja Trifkovic,
• Tong Wang, Lavanya Babujee, Robert Presler Jr., Randall Dahn, Yasuo Suzuki, Peter J. Halfmann, Seiya Yamayoshi, Gabriele Neumann &
• Yoshihiro Kawaoka

Nature (2024)Cite this article​

Last July we looked at an earlier study (see Nature Comms: Pathogenicity and Transmissibility of Bovine H5N1 Influenza Virus) which found this virus was less lethal, and did not transmit efficiently via the respiratory route to ferrets.

From this NIH review, we learn that this virus may be more formidable than previously thought, and that our mainstay influenza antiviral - oseltamivir (aka `Tamiflu') - may not be as effective as some newer options (i.e. favapirivir and baloxavir).

The `money quote' from these researchers is `. . . based in these observations, every effort should be made to contain HPAI H5N1 outbreaks in dairy cattle to limit the possibility of further human infections.”​

A goal which, right now, we seem to be falling well short of.

Bovine H5N1 influenza from infected worker transmissible and lethal in animal models

Some antiviral drugs highly effective against bovine H5N1​

What

A highly pathogenic avian influenza (HPAI) H5N1 virus, isolated from the eye of a farm worker who became infected through contact with dairy cows, was lethal in mice and ferrets infected in a high-containment laboratory environment, according to a new study in Nature. The study investigators also found that the virus isolated from the worker, who experienced mild inflammation of the cornea (conjunctivitis), could be transmitted through the air between separated ferrets and might be capable of binding to and replicating in human respiratory tract cells.

The virus isolated from the worker is called huTX37-H5N1 and has a mutation (PB2-E627K) frequently seen in avian influenza viruses that replicate in mammal

“based in these observations, every effort should be made to contain HPAI H5N1 outbreaks in dairy cattle to limit the possibility of further human infections.”

s, typically making virus replication more efficient. These mutations underscore the need for continued monitoring and evaluation of viruses from the current H5N1 outbreak.

The study also showed that a bovine H5N1 virus is susceptible to the antiviral drugs favipiravir and baloxavir marboxil (brand name Xofluza) of the polymerase inhibitor class, as well as the neuraminidase inhibitor zanamivir. The virus is less sensitive to oseltamivir (Tamiflu), another neuraminidase inhibitor.

In laboratory experiments, huTX37-H5N1 replicated in human cornea and lung cells. The scientists determined the lethal dose of huTX37-H5N1 as less than 1 plaque-forming unit (PFU) in mice, compared to 31.6 PFU as the lethal dose of a bovine H5N1 virus isolated from the milk of a lactating cow. The huTX37-H5N1 virus also infected each of 15 different mouse tissues tested, with the highest virus levels found in respiratory tissues.

Researchers also infected ferrets with a high dose of huTX37-H5N1. Flu infections in ferrets more closely resemble human flu infections than those in mice. All infected ferrets died within 5 days and scientists found huTX37-H5N1 virus in all the tissues sampled, with high levels in the respiratory system. In a prior study, the researchers had infected ferrets with a bovine H5N1 virus and, although it caused severe disease, lethality was limited.

To evaluate respiratory transmission, the scientists placed healthy ferrets in cages about 5 centimeters away from ferrets infected one day earlier with one of four decreasing doses of huTX37-H5N1. All directly infected ferrets died within 6 days and, depending on the exposure dose, between 17% and 33% of the nearby animals became infected via respiratory droplet transmission. These results indicate that a bovine HPAI H5 virus isolated from an infected person can transmit among mammals via respiratory droplets, though with limited efficiency.

The authors note that the person infected with the huTX37-H5N1 virus did not develop severe illness. In fact, human cases reported from the current outbreak have mostly experienced conjunctivitis and/or mild respiratory symptoms. The researchers speculate that eye infection with a low dose of bovine H5N1 virus might result in localized conjunctivitis without severe disease in humans. Multiple exposures to seasonal human influenza viruses, they say, might provide people with low levels of protection against currently circulating HPAI H5N1 viruses—though additional study is needed.

In summary, this study characterizes the huTX37-H5N1 isolate, finding that it may be capable of replicating in cells of the respiratory tract in humans, that it is pathogenic in mice and ferrets, and that it is capable of being transmitted by the respiratory route in ferrets.

“based in these observations, every effort should be made to contain HPAI H5N1 outbreaks in dairy cattle to limit the possibility of further human infections.”
Scientists from the University of Wisconsin at Madison led the research with collaborators from Shizuoka and Tokyo Universities and the Research Center for Global Viral Diseases in Japan. The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, funded much of the work through its Centers of Excellence for Influenza Research and Response program.
​

Articles

C Gu et al. A human isolate of bovine H5N1 is transmissible and lethal in animal models. Nature DOI: 10.1038/s41586-024-08254-7 (2024).

A Eisfeld et al. Pathogenicity and transmissibility of bovine H5N1 influenza virus in mice and ferrets. Nature DOI: 10.1038/s41586-024-07766-6 (2024).


​

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https://afludiary.blogspot.com/2024/10/nature-human-isolate-of-covine-h5n1-is.html
​

 

[Pathfinder]

NOVEMBER 1, 2024
ESPAÑOL
​

CDC Reports Additional Avian Influenza A(H5N1) Ferret Study Results

WHAT TO KNOW


The results of CDC's first study looking at the effects on ferrets of an avian influenza A(H5N1) virus from a human case in Texas have been published in Nature. CDC first shared preliminary findings from this study, which were instrumental in informing early risk assessments related to this outbreak, in June 2024. Ferrets are used as a model to assess the disease and spread characteristics of specific influenza (flu) viruses in people. The initial study was subsequently replicated to confirm the findings, and this publication summarizes all the findings from the ferret experiments using the isolate from the case human case in Texas. Results of subsequent similar studies using different viruses from the same outbreak have differed.

Summary of cumulative findings

• These ferret study findings are now available in the peer reviewed literature in Nature.
• The study used an avian influenza A(H5N1) virus from the first human case associated with the current outbreak in U.S. dairy cattle and poultry, which occurred in Texas (A/Texas/37/2024).
• That virus caused severe illness and death in 100% of infected ferrets causing more severe disease compared to other avian influenza A(H5N1) viruses in the same genetic group isolated prior to the 2024 dairy cow outbreaks. This also is different from what is seen with seasonal influenza viruses, which make ferrets sick, but are not fatal to ferrets.
• The A/Texas/37/2024 virus spread efficiently between ferrets in direct contact (100%) but did not spread efficiently between ferrets via respiratory droplets (i.e., droplets containing virus released into the air from coughs or sneezes) or by fomites (i.e., contaminated surfaces) (66%). This is different from what is seen with seasonal influenza viruses, which do spread efficiently via respiratory droplets and fomites in ferrets (100%).
• Results from this ferret study helped inform CDC's early risk assessments of the potential impact of these viruses on human health.
• The results suggest this virus has the potential to cause severe illness in people and reinforce the importance of protective measures among people with exposure to infected animals and for public health and agriculture communities to continue to work together to contain this outbreak.
• The preliminary results of this study reported in June 2024, are available at CDC Reports A(H5N1) Ferret Study Results | Bird Flu | CDC.

CDC researchers used a ferret model 1to better understand the severity of illness and efficiency of transmission of A/Texas/37/2024, the avian influenza A(H5N1) virus isolated from a sick dairy cow worker in Texas on April 1, 2024. This was the first human case associated with the ongoing multistate outbreak of H5 bird flu among dairy cows and poultry. CDC researchers subsequently repeated parts of the study using additional animals to confirm the findings. (Like humans, different ferrets can respond differently to infection, and some ferrets may spread more virus than others. This is why a series of experiments are conducted and the results are combined.)

Severity of Disease


Similar to the preliminary results in six ferrets, all six infected ferrets in confirmatory testing experienced severe disease and died, highlighting the potential for this virus to cause severe disease in humans. The results are consistent with findings from other studies of ferrets infected with avian influenza A(H5N1) viruses, including two published studies conducted during the past year. Ferrets infected with avian influenza A(H5N1) viruses from mink in Spain (A/mink/Spain/3691-8_22VIR10586-10/2022) and from a person in Chile (A/Chile/25945/2023) had severe illness that was either fatal or required euthanasia. However, subsequent studies at CDC using A(H5N1) viruses from Michigan, have differed, with ferrets experiencing milder illness. None of the ferrets infected with the A/Michigan/90/2024 virus died or had to be euthanized because of severe illness.

Spread via Direct Contact


The initial study found that the A/Texas/37/2024 virus spread easily among ferrets (3 of 3 ferrets, or 100%) in direct contact with infected ferrets placed in the same enclosure.

Spread via Respiratory Droplets


The virus was less capable of spreading by respiratory droplets compared to seasonal influenza viruses. This was tested by placing infected ferrets in enclosures next to healthy ferrets (with shared air but without direct contact). In that situation, 4 of 6 ferrets (66%) became infected, and there was a one- or two-day delay in transmission with the A/Texas/37/2024 virus compared to transmission with seasonal influenza viruses. The observed capacity of avian influenza A(H5) virus to transmit via respiratory droplets in ferrets has not been frequently reported in the past. The last time this level of transmission was observed was a ferret study done on A/Hong Kong/486/97, an avian influenza A(H5N1) virus isolated from a human in 1997. That study also found respiratory droplet spread occurred in 2 of the 3 ferrets (66%). The older 1997 avian influenza A(H5N1) virus did not result in efficient spread among people, and person-to-person spread has not been observed with avian influenza A(H5N1) viruses since 2007. This suggests that A/Texas/37/2024-like viruses would need to undergo changes to spread efficiently by droplets through the air, such as from coughs and sneezes like in the way seasonal influenza viruses spread.

Spread via Fomites


These ferret experiments also tested the ability of the virus to spread in a fomite transmission model (contaminated surfaces). When healthy ferrets were placed in a contaminated cage (with contaminated bedding, food, water, etc.), 1 out of 3 became infected. With a seasonal influenza virus, 3 out of 3 ferrets were positive in the fomite transmission model.

Exhaled Virus Measurements


The ferret experiments also measured the amount of virus exhaled from infected ferrets into the air. Ferrets infected with A/Texas/37/2004 exhaled comparatively more virus into the air than was observed with A/Michigan/90/2024 and A/Chile/25945/2023.

Genetic Characteristics of the Virus


The A/Texas/37/2024 virus is a genetic outlier of this group of avian influenza A(H5N1) viruses. It has two mammalian adaptive mutations not seen in the other A(H5N1) viruses that have been genetically sequenced in association with the current outbreak in dairy cows. Sequencing showed changes in two polymerase proteins, the PB2 gene at position E627K and the PA gene at position K142E:

• The polymerase PB2 E627K mutation has been previously identified to cause greater virus replication in mammals and more severe disease.
• The polymerase PA K142E gene change has been previously associated with enhanced virulence in mammalian hosts when combined with the PB2-627 mutation.

Changes like those seen in the A/Texas/37/2024 virus may help the virus replicate better in mammals and humans. The results of these experiments were used to inform an ongoing, broader CDC-led influenza risk assessment (IRAT) on A/Texas/37/2024.

Limitations of ferret experiments


For decades, CDC has conducted these types of studies to inform risk assessments of influenza viruses with pandemic potential. The use of robust and genetically diverse animal models as subjects is preferred in many areas of research. The ferrets used in our studies are outbred (bred to have genetic diversity) animals whose response to influenza virus infection is generally very similar to that of humans; therefore, it is expected that there will be some variability in disease outcomes and immune responses. This is why the experiments were repeated. The major benefit of using an outbred ferret model is that it better mimics the human population, which is genetically diverse. The conclusions obtained from studies using outbred animal models are more representative and generalizable across different experimental conditions and populations. Even as a well-documented and commonly used research model for human illness and transmission, there are limitations to ferret experiments.

• Animals did not possess any antibodies to influenza A virus before infection, so this does not capture any potential/unknown contributions of pre-existing immunity that may be present in human populations at large.
• Ferrets in this study were deliberately administered a large quantity of virus. While the virus is transmitted in the respiratory droplet model when administered in a large quantity, it's unclear whether similar transmission levels would be observed following lower amounts of virus.
• The conclusions obtained from studies using outbred animal models are more representative and generalizable across different experimental conditions and populations.
• The number of animals used in the studies could be considered a limitation; however, CDC researchers comply with the 3Rs (Replace, Reduce, Refine) principles that govern ethical and humane animal research. Therefore, CDC studies use only the smallest possible number of animals necessary to meet research goals.

Conclusion and risk assessment


Overall, the cumulative results of studies in ferrets using the A(H5N1) virus from a human case in Texas suggest the virus still is not capable of spreading efficiently among people via respiratory droplets compared to seasonal influenza viruses. These findings highlight the importance of continued surveillance to monitor these kinds of changes in circulating A(H5N1) viruses. More information on ferret studies is available at CDC Reports A(H5N1) Ferret Study Results | Bird Flu | CDC.
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https://www.cdc.gov/bird-flu/spotlights/ah5n1-ferret-study-results.html